This invention relates to the synthesis of polymers which contain non-thrombogenic (NON-TB) as well as anti-thrombogenic (ANTI-TB) properties. Such polymers can be conveniently represented as follows:
In schematic diagrams of this kind, as used herein, the designated side chains or groups can occur in any order and in any relative proportions along the polymer backbone.
In polymers of Type 1 the non-thrombogenic (NON-TH) component may consist of non-ionic hydrophilic domains, ionic domains, zwitterionic domains or combinations of such domains. In novel Type 1 polymers in accordance with the invention, such non-thrombogenic components may be selected from, but are not limited to, polymerizable sulphonates, polymerizable sulphates, polymerizable N-sulphates (also known as sulphamates), polymerizable zwitterionic compounds, and polymerizable polyethylene glycols. When we synthesized polymers of Type 1, without the anti-thrombogenic component, and coated various medical devices, we found blood cell and protein deposition reduced by greater than 90%. Greatly reduced ( greater than 95%) activation of white cells, platelets and complement was observed. This type of synthetic polymer can be described as a non-thrombogenic polymer.
The non-thrombogenic Type 1 polymer, as described, was synthesized with polymerizable heparin to give a Type 2 polymer. Surprisingly, the activity of the heparin was retained in the Type 2 polymer and such polymers, when coated on to medical devices, had the additional property of reducing the thrombin-antithrombin complex concentration. This inclusion of heparin into the non-thrombogenic polymer gave a new polymer which additionally exhibited anti-thrombogenic properties.
Another aspect of this invention is the process by which the non-thrombogenic and anti-thrombogenic polymers are coated onto medical devices.
There is a growing interest in the use of artificial materials in clinical practice where these materials are in continuous contact with blood. Medical devices made from these materials are required to perform in the harsh biological environment in a specific application, for a specific duration without stimulating a biological response which may prove to be detrimental. Hence, such devices are required to be accepted by the biological environment for a specific application and duration, i.e., need to be bioacceptable. Improvements in bioacceptability are highly desirable for medical devices manufactured from artificial materials. Such materials commonly include polyvinyl chloride, polyethylene, polypropylene, polyurethanes, polycarbonates, stainless steel, silicones and the like. The biological response to blood contact with an artificial surface can be regarded in terms of different contributions from protein, platelet and blood cell deposition, together with platelet and blood activation leading to thrombus formation.
Many investigations have been carried out to prevent an artificial surface from provoking thrombus formation, i.e., to form a bioacceptable surface. Such investigations include the use of polymers which are natural, hydrophilic, hydrophobic, zwitterionic and charged (anionic and cationic). These types of polymers are non-thrombogenic, have had limited success and therefore application. Surface modification of an artificial material by heparin (i.e., formation of an anti-thrombogenic surface) has also proved to be intractable. Although clot formation has been reduced, platelet activation and blood cell activation are however still prevalent. Similarly, a particular artificial surface may be resistant to protein, platelet and blood cell deposition but may still activate blood constituents.
Each surface, whether non-thrombogenic or anti-thrombogenic, has its own profile of desirable bioacceptable properties, but no particular material possesses the full spectrum of the desired properties.
Additional disadvantages of some of the known approaches are (i) the procedures used to produce these materials are complex, (ii) the methods of applying these materials to the medical device are elaborate, and (iii) these processes utilize reagents which are highly toxic, even in minute quantities.
In a new approach to the problem of finding suitable bioacceptable materials, we have synthesized a novel non-thrombogenic polymer, and have also modified non-thrombogenic polymers by incorporating a polymerizable anti-thrombogenic compound, exemplified by polymerizable heparin. It was found that heparin activity was maintained, while the non-thrombogenity of the polymer component was prevalent. Other known biologically active anti-thrombogenic compounds include hirudin, warfarin and hyaluronic acid, and can be used in the same manner as the polymerizable heparin.
The invention provides a medical device which comprises a polymer coating, the polymer coating comprising a polymer comprising a polymer backbone and having at least two pendant groups selected from:
(a) a polyoxyalkylene ether group,
(b) a sulphate group,
(c) a sulphonate group, or
(d) a sulphamate group,
wherein the polymer is produced by polymerizing monomers having such groups.
The invention also provides a medical device which comprises a polymer coating, the polymer coating comprising a polymer comprising a polymer backbone and having at least two pendant groups selected from:
(a) a polyoxyalkylene ether group,
(b) a sulphate group,
(c) a sulphonate group,
(d) a sulphamate group, or
(e) a zwitterionic group,
wherein the polymer coating is produced by polymerizing monomers having such groups.
The invention provides a polymer comprising a polymer backbone and having at least two pendant groups selected from:
(a) a polyoxyalkylene ether group,
(b) a sulphate group,
(c) a sulphonate group, or
(d) a sulphamate group,
wherein the polymer further comprises a pendant heparin group, and wherein the polymer is produced by polymerizing monomers having such groups.
Additional features and advantages of the invention are set forth in the description which follows and in part will be apparent from the description. The objectives and other advantages of the invention will be realized and attained by the medical devices, polymers, coatings, and methods of the invention as particularly pointed out in the written description and claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
The invention provides a medical device which comprises a polymer coating, the polymer coating comprising a polymer comprising a polymer backbone and having at least two pendant groups selected from:
(a) a polyoxyalkylene ether group,
(b) a sulphate group,
(c) a sulphonate group, or
(d) a sulphamate group,
wherein the polymer is produced by polymerizing monomers having such groups. In one embodiment of the invention, the polymer comprises a pendant polyoxyalkylene ether group. In another embodiment of the invention, the polymer does not comprise a pendant sulphonate group. In yet another embodiment of the invention, the polymer comprises a pendant polyoxyalkylene ether group and does not comprise a pendant sulphonate group. In one embodiment of the invention, the medical device is a blood oxygenator. In one embodiment of the invention, the polymer comprises a pendant heparin group; in another, the polymer comprises a pendant hirudin, warfarin, or hyaluronic acid group.
The invention provides a method of making a medical device which comprises a polymer coating comprising:
providing a mixture of monomers comprising at least two of the following monomers:
(a) a monomer having a polyoxyalkylene ether group,
(b) a monomer having a sulphate group,
(c) a monomer having a sulphonate group, or
(d) a monomer having a sulphamate group;
coating the mixture of monomers onto a medical device; and
polymerizing the mixture of monomers to form a polymer coating, wherein the mixture of monomers can comprise only monomers or can be partially prepolymerized. In one embodiment of the invention, the polymer comprises a pendant polyoxyalkylene ether group. In another embodiment of the invention, the polymer does not comprise a pendant sulphonate group. In yet another embodiment of the invention, the polymer comprises a pendant polyoxyalkylene ether group and does not comprise a pendant sulphonate group. In one embodiment of the invention, the medical device is a blood oxygenator. In one embodiment of the invention, the polymer comprises a pendant heparin group; in another, the polymer comprises a pendant hirudin, warfarin, or hyaluronic acid group.
The invention provides a medical device which comprises a polymer coating, the polymer coating comprising a polymer comprising a polymer backbone and having at least two pendant groups selected from:
(a) a polyoxyalkylene ether group,
(b) a sulphate group,
(c) a sulphonate group,
(d) a sulphamate group, or
(e) a zwitterionic group,
wherein the polymer coating is produced by polymerizing monomers having such groups. In one embodiment of the invention, the polymer comprises a pendant polyoxyalkylene. ether group. In another embodiment of the invention, the polymer does not comprise a pendant sulphonate group. In yet another embodiment of the invention, the polymer comprises a pendant polyoxyalkylene ether group and does not comprise a pendant sulphonate group. In one embodiment of the invention, the medical device is a blood oxygenator. In one embodiment of the invention, the polymer comprises a pendant heparin group; in another, the polymer comprises a pendant hirudin, warfarin, or hyaluronic acid group.
The invention provides a polymer comprising a polymer backbone and having at least two pendant groups selected from:
(a) a polyoxyalkylene ether group,
(b) a sulphate group,
(c) a sulphonate group, or
(d) a sulphamate group,
wherein the polymer further comprises a pendant heparin group, and wherein the polymer is produced by polymerizing monomers having such groups. In one embodiment of the invention, the polymer comprises a pendant polyoxyalkylene ether group. In another embodiment of the invention, the polymer does not comprise a pendant sulphonate group. In yet another embodiment of the invention, the polymer comprises a pendant polyoxyalkylene ether group and does not comprise a pendant sulphonate group. The invention also provides a coating material comprising the polymer described above.
The invention also provides a polymer comprising a polymer backbone and having at least two pendant groups selected from:
(a) a polyoxyalkylene ether group,
(b) a sulphate group,
(c) a sulphonate group, or
(d) a sulphamate group,
wherein the polymer further comprises a pendant hirudin, warfarin, or hyaluronic acid group, and wherein the polymer is produced by polymerizing monomers having such groups.
One embodiment of the present invention provides polymers comprising a polymer backbone having pendant groups, obtainable by polymerizing monomers having such groups, characterized in that said polymers are obtained by copolymerizing monomers of at least three different classes selected from:
(a) monomers having sulphate groups
(b) monomers having sulphonate groups
(c) monomers having sulphamate groups, and
(d) monomers having polyoxyalkylene ether groups.
Another embodiment of the present invention provides polymers comprising a polymer backbone having pendant groups, obtainable by polymerizing monomers having such groups, characterized in that said polymers are obtained by copolymerizing monomers of at least three different classes selected from:
(a) monomers having sulphate groups
(b) monomers having sulphonate groups
(c) monomers having sulphamate groups
(d) monomers having polyoxyalkylene ether groups, and
(e) monomers having zwitterionic groups.
A further embodiment of the present invention provides a method of forming a coating of a polymer as described above on a medical device by forming an ungelled partial polymer by reacting a solution of an amine polymer with a crosslinking agent, activating the medical device by solution coating with said partial polymer, and depositing the polymer on the resulting activated medical device.
The present invention also provides a coating material comprising a polymer as described above.
Without wishing to be bound by any theory or explanation of the invention, it appears that non-thrombogenic surfaces have an important impact on the first event of contact of blood with an artificial surface. This event occurs almost instantaneously and consists of protein adsorption. Subsequent events are largely determined by interactions of blood with the adsorbed protein. The nature of the artificial surface determines the manner and extent of protein attachment.
For hydrophobic surfaces, attachment occurs by hydrophobic interactions with the protein, which causes conformational change of the adsorbed protein, exposing sites for protein interaction resulting in further protein adsorption. The next sequence of events has a pronounced influence in promoting platelet adsorption/activation and white cell adsorption/activation. The consequence of these events is the formation of thrombus.
Protein adsorption on hydrophilic surfaces is more readily and rapidly reversible than on hydrophobic surfaces. The extent of reversibility is determined by the nature of the chemical bond in the equilibrium state. At high states of reversibility, protein adsorption is not prevalent and consequently platelet and white cell adsorption/activation is prevented. Therefore, thrombus formation is averted.
This type of hydrophilic surface is regarded as being non-thrombogenic and in this respect we have found a new artificial hydrophilic polymer with at least three different types of hydrophilic groups which include, but are not restricted to, sulphonate, sulphate, N-sulphate (sulphamate) or zwitterionic groups, and polyethylene glycol or glycol ether units in the same polymer backbone.
In one embodiment of the present invention the non-thrombogenic polymer is obtainable by radical polymerization, preferably of monomers having reactive carbon-carbon double bonds to form the polymer backbone and said monomer constituents containing, but not limited to, sulphonates, sulphates, N-sulphates (sulphamates), zwitterions, and polyethylene glycol units, these monomer constituents being contained in the same polymer composition. Such monomers may be separated into three groups.
The first group is based on monomers derived from acrylates or methacrylates of sulphonates, sulphates and N-sulphates:
CH2xe2x95x90CR1xe2x80x94C(xe2x95x90O)xe2x80x94Z1xe2x80x94R2xe2x80x94Y1xe2x80x94X1xe2x80x83xe2x80x831)
Where R1 is H or CH3;
R2 is a linear or branched alkylene of 2-10 carbon atoms, phenylene, phenyl alkylene with 1-10 carbon atoms in the alkylene structure or the polyoxyalkylene structure [CH2CHR1xe2x80x94O]n where R1 is H or CH3 and n is from 2 to 50; Z1 is oxygen (xe2x80x94Oxe2x80x94) to give an ester linkage or secondary amine (xe2x80x94NHxe2x80x94) to give an amide linkage; Y1 is (xe2x80x94Oxe2x80x94) or (xe2x80x94NHxe2x80x94) or is absent; and
X1 is sulphonate (xe2x80x94SO3) together with an acceptable balancing cation.
The second group is based on monomers derived from vinyl, allyl or methyl allyl, of sulphonates, sulphates and N-sulphates:
CH2xe2x95x90CR1xe2x80x94R2xe2x80x94Y1xe2x80x94X1xe2x80x83xe2x80x832)
Where R1 is H or CH3; R2is a linear or branched alkylene of 1-10 carbon atoms, phenylene, phenyl alkylene with 1-10 carbon atoms in the alkylene structure or the polyoxyalkylene structure [CH2xe2x80x94CHR1xe2x80x94O)]n, where R1 is H or CH3 and n is from 2 to 50; Y1 is (xe2x80x94Oxe2x80x94) (xe2x80x94NHxe2x80x94) or is absent; and X1 is sulphonate (xe2x80x94SO3xe2x80x94) together with an acceptable balancing cation.
In both groups of monomers (1) and (2), when Y1 is (xe2x80x94Oxe2x80x94), the monomer terminates in a sulphate group; Y1 is (xe2x80x94NHxe2x80x94), the monomer terminates in a N-sulphate group; R2 and Y1 are not present, the monomer terminates in a sulphonate group; R2 is polyoxyalkylene and Y1 is not present, the monomer terminates in a sulphate group.
The third group of monomers is derived from acrylates or methacrylates of polyoxyalkylene glycols or glycol ethers:
CH2xe2x80x94CR3xe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94[CH2xe2x80x94CHR4xe2x80x94O]nxe2x80x94R7xe2x80x83xe2x80x833)
Where R3 and R4, which may be the same or different, are each H or CH3, R7 is H or alkyl with 1 to 5 carbon atoms, e.g., methyl, and n is an integer from 2 to 50.
Monomer examples incorporating sulphonate groups include, but are not restricted to, salts of: 2-sulphoethyl methacrylate, 2-sulphoethyl acrylate, 3-sulphopropyl methacrylate, 3-sulphopropyl acrylate, vinyl sulphonate, allyl sulphonate, methyl allyl sulphonate, p-styrene sulphonate, 2-acrylamido-methylpropanesulphonate, 3-sulphopropyl ethoxy methacrylate, 3-sulphopropyl ethoxy acrylate, 3-sulphopropyl polyoxyalkylene methacrylate, 3-sulphopropyl polyoxyalkylene acrylate.
Similarly, examples of monomers terminating in sulphate groups include, and are not confined to, salts of: 2-sulphatoethyl methacrylate, 2-sulphatoethyl acrylate, 3-sulphatopropyl methacrylate, 3-sulphatopropyl acrylate, 4-sulphatobutyl methacrylate, 4-sulphatobutyl acrylate, allyl sulphate, methyl allyl sulphate, 3-buten-1-sulphate, 3-buten-2-sulphate, 2-methyl-2-propanol-sulphate, 2-methyl-3-buten-1-sulphate, 3-methyl-3-buten-1-sulphate, 2-sulphatoethyl methacrylamide, 2-sulphatoethyl acrylamide, 3-sulphatopropyl methacrylamide, 3-sulphatopropyl acrylamide, 4-sulphatobutyl methacrylamide, 4-sulphatobutyl acrylamide, sulphato polyoxyalkylene methacrylate, sulphato polyoxyalkylene acrylate.
Examples of N-sulphate (sulphamate) containing monomers include, but are not limited to, salts of: 2-sulphamatoethyl methacrylate, 2-sulphamatoethyl acrylate, 3-sulphamatopropyl methacrylate, 3-sulphamatopropyl acrylate, 4-sulphamatobutyl methacrylate, 4-sulphamatobutyl acrylate, allyl sulphamate, methyl allyl sulphamate, 2-sulphamatoethyl methacrylamide, 2-sulphamatoethyl acrylamide, 3-sulphamatopropyl methacrylamide, 3-sulphamatopropyl acrylamide, 4-sulphamatobutyl methacrylamide, 4-sulphamatobutyl acrylamide, sulphamato polyoxyalkylene methacrylate, sulphamato polyoxyalkylene acrylate.
The salts used to form the polymers according to the invention, including those listed above, will have an acceptable, especially physiologically acceptable, balancing cation such as an alkali metal (e.g., sodium) cation, or an ammonium or substituted ammonium cation. Hydrogen cations usually provide a polymer that is too acidic for the preferred use.
Other examples of non-thrombogenic polymers include those in which zwitterionic monomers may be included in the above formulations. For example, the non-thrombogenic polymers can contain any zwitterionic monomer as an integral part of the polymer backbone. The zwitterionic monomers may also be included in the non-thrombogenic/antithrombogenic polymers. Such zwitterionic monomers include, but are not limited to, 2-(methacryloyloxyethyl)-2xe2x80x2-(trimethylammonium) ethyl phosphate inner salt and dimethyl (2-methacryloylethyl)-[1-(2-sulphopropyl)] ammonium betaine inner salt.
A wide range of monomer compositions can be utilized in the formation of the non-thrombogenic polymer. Such a polymer may contain, and is not limited to, 3 to 4 different monomer constituents. The ter-polymer (3 different monomers) and the tetra-polymer (4 different monomers) are formulated from 3 or 4 respectively of at least one sulphate monomer type, at least one sulphonate monomer type, at least one sulphamate monomer type, and at least one polyoxyalkylene monomer type in the final polymer composition. This polymer composition can accordingly be schematically represented as follows, where the relative frequency and the order of occurrence of each monomer type are variable (being random co-polymers). In each instance anions shown are balanced by acceptable cations, such as those mentioned above.
The above co-polymerized monomer compositions are examples of non-thrombogenic (NON-TH) polymers represented above as Type 1.
In another aspect of this invention the non-thrombogenic component is accompanied by a polymerizable anti-thrombogenic component such as polymerizable heparin in the same polymer backbone, and said anti-thrombogenic component in its bioactive form being carried by an integral part of the aforementioned polymer backbone.
Functionalization of heparin by methacrylation of heparin is known (ACS Symposium Series 77; Carbohydrate Sulphates, 1978). Subsequent known polymerizations with other monomers give rise to anti-thrombogenic polymers only, containing no non-thrombogenic component (of the kind referred to herein).
This aspect of this invention accordingly provides a polymer containing non-thrombogenic and anti-thrombogenic constituents on the same polymer backbone. Preferred non-thrombogenic constituents may comprise sulphate, sulphamate, sulphonate, zwitterionic and polyoxyalkylene glycol and glycol ether, together with anti-thrombogenic constituents consisting of polymerizable heparin bearing carbon-carbon double bonds. Essentially the carbon-carbon double bond carried by the heparin moiety is polymerizable by a free radical process and may be by way of example vinyl, allyl, methyl allyl, acrylate or polymerizable methacrylate. Heparin linked to a component containing a carbon-carbon double bond is hereafter referred to as heparin monomer, corresponding monomers in which the heparin is replaced by hirudin, warfarin or hyaluronic acid moieties may be used in like manner.
The favored heparin monomers are those in which heparin is linked to a polyoxyalkylene methacrylate or polyoxyalkylene acrylate through an ester or carbonate linkage. The ester or carbonate linkage is formed by activating the hydroxyl terminating polyoxyalkylene methacrylate or acrylate with carbonyldiimidazole, forming the activated imidazoyl carbonate, which subsequently is either coupled to carboxylic groups of the heparin molecule to yield an ester linkage or coupled to hydroxyl groups of the heparin molecule to yield a carbonate linkage. This means of attaching the polyoxyalkylene methacrylate or acrylate group to heparin allows polymerization of the heparin with the desired biological properties. Other coupling techniques as described in WO 91/16932 using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide result in linkages occurring on sulphate groups of the heparin, called a sulphonamide linkage. This coupling procedure results in poor biological properties since these N-sulphate and sulphate groups are important for binding to antithrombin.
Preferred heparin monomers include those of the following formula:
With ester linkage to heparin:
CH2xe2x95x90CR5xe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94CH2xe2x80x94CHR6xe2x80x94[Oxe2x80x94CH2xe2x80x94CHR6xe2x80x94]nxe2x80x94Oxe2x80x94C(xe2x95x90O)-Heparinxe2x80x83xe2x80x83(1)
With carbonate linkage to heparin:
CH2xe2x95x90CR5xe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94CH2xe2x80x94CHR6xe2x80x94[Oxe2x80x94CH2xe2x80x94CHR6xe2x80x94]nxe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94O-Heparinxe2x80x83xe2x80x83(2)
In both general formulae, R5 and R6, which may be the same or different, are each H or CH3; and n is an integer from 0 to 49.
Particularly preferred heparin monomers are those derived from polyethylene oxide units, that is to say where R2 is H.
The heparin monomers (1) and (2), as above, are novel and are other aspects of this invention and may be produced by reacting hydroxyl terminated polyoxyalkylene with carbonyldiimidazole [Imxe2x80x94C(xe2x95x90O)xe2x80x94Im] to form the activated imidazoyl carbonate: CH2xe2x95x90CR5xe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94CH2xe2x80x94CHR6xe2x80x94[Oxe2x80x94CH2xe2x80x94CHR6xe2x80x94]nxe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94Im, where R5, R6 and n have the meanings given above, this being followed by the coupling of the activated imidazoyl carbonate to heparin under basic pH conditions using bicarbonate buffer at room temperature.
The heparin monomer is polymerized with the aforementioned monomer of sulphate, sulphamate, sulphonate and polyoxyalkylene, producing a polymer with both non-thrombogenic and anti-thrombogenic properties. This polymer composition may contain 4 to 5 of the different types of monomer constituent. The tetra-polymer (4 different monomer types) and the penta-polymer (5 different monomer types) are so formulated from 3 or 4 respectively of at least one sulphate monomer type, at least one sulphonate monomer type, at least one sulphamate monomer type, and at least one polyoxyalkylene monomer type, together with at least one heparin monomer type, in the final polymer composition. This polymer composition can accordingly be schematically represented as follows, the relative frequency and the order of occurrence of each monomer type being variable. In each instance the anions shown are balanced by acceptable cations, such as those mentioned above.
These non-thrombogenic/anti-thrombogenic (NON-TH/ANTI-TH ) polymers are of the kind represented above as Type 2.
Polymerization may be carried out by conventional aqueous solution polymerization using a water soluble initiator, such as potassium persulphate, after degassing the solution and under an inert gas, such as nitrogen. Reaction temperature for polymerization is at room or elevated temperature, provided that the heparin biological activity is not affected. The preferred polymerization temperature is one between 15 to 90xc2x0 C., and generally a polymerization temperature of 75xc2x0 C. is suitable. The polymer may be purified by conventional means, such as precipitation, filtration wash and dialysis.
The aforementioned non-thrombogenic polymer or the non-thrombogenic/anti-thrombogenic polymer according to the invention is capable of being applied as a coating on medical devices for use in blood-contacting applications. In this regard, another aspect of this invention is the modification of polyethylene imine or other primary or secondary amino containing polymers to an extent that they form a stable attachment between the medical device and the non-thrombogenic polymer or the non-thrombogenicxe2x80x94anti-thrombogenic polymer.
The use of unmodified polyethylene imine as an anchoring point for heparin is known, EP 0124676. In these processes the medical device requires chemical pre-treatment to allow attachment of polyethylene imine to occur. Additionally, multi-layers are built up on the device to ensure good coverage and to enhance the stability of the attachment. These are disadvantages which have severe impact on the performance and the coating process. The heparin attached is grafted onto the external polyethylene imine layer where surface covering is limited. There is predominantly preferential ionic bonding of the heparin to the polyethylene imine. In such instances the heparin may be released from the surface. This coating requires repeated steps to ensure that the polyethylene imine is bound effectively. This has the constraint of increasing the complexity of the process which results in high costs being incurred.
To overcome the disadvantages mentioned above we have devised a method for modifying primary or secondary amine polymers including polyethylene imine which can be attached to the medical device without any pre-treatment and can be carried out in a single step. This is achieved by increasing the molecular weight of the amine polymer, but to a limited extent, whereby the polymer does not gel, but remains in solution. This can, for instance, be achieved by crosslinking the amine, e.g., by treatment with a crosslinking agent, such as an alkylene diisocyanate, and/or with an alkyl isocyanate. The isocyanate crosslinking agents mentioned above react very quickly with the amino groups, but other crosslinking agents that are reactive with amino groups may be employed. These include, but are not limited to, diacids, diacid chlorides and cyclic anhydrides or dianhydrides. Generally there will be 4 to 16 carbon atoms between the active groups of the crosslinking agents. By increasing the hydrophobic nature of the amine polymer in this manner, it is capable of attaching to a suitable medical device sufficiently to allow attachment of the non-thrombogenic polymer or the non-thrombogenic/antithrombogenic polymer. Hence the polymer coating process is essentially achieved in two steps, as opposed to multiple steps.
Attachment of the polymer to the polyethylene imine pre-coating can be enhanced by the incorporation of acrolein in the monomer feed for the non-thrombogenic/anti thrombogenic polymer, giving aldehydic groups on the polymer backbone. These products are also novel. The aldehydic groups are allowed to react with amino groups on the modified polyethylene imine to form a Schiff""s base which is reduced to form a stable covalent bond. Alternatively the non-thrombogenic/anti-thrombogenic polymer may be attached to the modified polyethylene imine by ionic interaction.
The invention is illustrated by the following Examples, which are not intended to restrict the scope of the invention. In the Examples, concentrations are expressed as percentages weight/volume, i.e. grams per 100 ml of solution.
The structure of the polymers whose preparation is identified in the following Examples can be confirmed by the presence of certain peaks in their FTIR spectra. These peaks include: